1. Field of the Invention
The present invention relates to a substrate processing apparatus for coating a semiconductor wafer with a resist and developing thereof in a fabrication of semiconductor device. In detail, the invention relates to a substrate processing apparatus that controls the atmosphere of the processing environment of the substrate.
2. Description of the Related Art
In a process of photolithography in the semiconductor device fabrication, the surface of a semiconductor wafer (hereinafter referred to as “a wafer”) is coated with a photo-resist, exposing a mask pattern on the resist, then developing thereof, forming a resist pattern on the wafer surface. The resist coating and development are performed in an integrated coating and developing processing apparatus including a thermal processing apparatus such as a heating processing apparatus or a cooling processing apparatus. The coating and developing apparatus is connected to the aligner through an interface portion and the semiconductor device fabrication is actually performed.
In the coating and developing apparatus, when processing of wafer is performed, in order to prevent impurity such as particles from adhering to the wafer, the air cleaned with an air cleaner is supplied to the inside of the coating and developing processing apparatus as a down flow of air current, so that the wafer is processed in the clean condition.
However, these days, laser-beam light source with a short wavelength like, for example, F2 excimer laser (157 nm) is used in an aligner to cope with the miniaturization of the devices, therefore in case that impurities of molecule level, which had not been a problem up to now, such as oxygen, ozone, water and organic matter, adheres on the resist film coated on the wafer in the steps performed before the exposure, absorption and scattering of light caused by the impurities tend to occur. When moisture adheres on the resist film, 2% of the light will be absorbed with film thickness of every 10 Å(1 mm), and when the water molecules exist scattering on the wafer surface, difference arises in amount of exposure between the portion with water molecules and the portion without the water molecules which causes deterioration in the uniformity of line width of the pattern. The down flow of the air described above is not able to remove the impurities of molecule level.